4G and 5G Backup Broadband: How It Works, What to Buy and What It Costs

Prices and plans were checked in November 2026. Mobile deals change weekly, so use the figures as a guide and confirm before you buy.

If you are still deciding whether you need a backup at all, start with the complete guide to broadband backup.

How mobile backup works in plain English

Fixed broadband reaches you through a cable in the ground or on a pole. Mobile broadband reaches you by radio from a mast. Because the two take different physical routes, a cut cable or a failed street cabinet does not affect the mobile path. That independence is the whole value of a mobile backup.

Every mobile backup is built from the same three parts:

1. A SIM, which is your account with a mobile network and the data allowance attached to it.
2. A modem, the radio that talks to the mast.
3. A router, which shares the connection with your devices over Wi-Fi or cable.

A phone running a hotspot is all three in one. A 4G router is a modem and router in one box. The backup add-ons sold by broadband providers are the same parts again, packaged and managed for you.

Failover is the automatic part. A router that supports it checks the main connection continuously. When the main line stops responding, the router sends traffic over the mobile connection instead. When the line recovers, it switches back, which is called failback. From your sofa, the Wi-Fi name stays the same and things carry on after a short pause.

Two side effects are normal. Live connections reset at the moment of the switch, so a video call may freeze for a few seconds and rejoin. And your public IP address changes, because you are now reaching the internet through a different network: a work VPN (virtual private network) will reconnect, and some sites may ask you to sign in again.

4G or 5G: which is enough for a backup?

Coverage favours 4G. Ofcom's Spring 2026 update, based on January 2026 data, found that every operator's 4G network reaches at least 99% of premises outdoors, and that 4G from at least one operator covers 96% of the UK's landmass. For 5G, individual operators cover between 76% and 94% of premises outdoors ¹.

Speed favours 5G, but a backup rarely needs it. Three and EE advertise average download speeds of around 150 Mb and 146 Mb for their 5G home broadband services ⁴. That matters if several people need to carry on streaming and downloading as normal. For keeping work going it is far more than required: Zoom's own guidance asks for 1.2 Mbps in each direction for a one-to-one 720p HD video call ⁷. A steady, modest 4G connection will carry several calls at once.

Hardware cost favours 4G. In November 2026 a TP-Link Archer MR600 4G router was listed at about £89 to £99, against roughly £180 and up for the 5G Archer NX200 and about £199 for the Deco X50-5G ¹³.

Buy 5G if one of these applies:

• You have a strong 5G signal indoors and want the backup to feel close to your normal connection for a whole household.
• The mobile connection will double as an everyday second line, not only an emergency one.
• 4G at your address is congested at the times you work, and a 5G test shows a clear improvement.

Otherwise, 4G does the job for less.

Check your signal first: coverage, indoor reception, choosing a network

Coverage statistics describe signal outside buildings ¹. Thick stone walls, foil-backed insulation and basement rooms can reduce it sharply indoors. Ten minutes of testing before you buy saves a return.

1. Look up your postcode on Ofcom's mobile coverage checker and on the operators' own checkers. Ofcom updates its checker with the data collected for its Connected Nations reports ¹.
2. Test where the router will live. Use a phone on the network you are considering, stand where the equipment would sit, and run a speed test. Repeat it in the evening and at the time of day you most need the connection.
3. Try more than one network. One-month SIMs are cheap enough to use as a trial ². A network that is excellent on your street can be poor at the back of your house.
4. Move before you buy more kit. A window sill or an upstairs room often gives a markedly better signal than a cupboard under the stairs.
5. Consider an external antenna only if the tests are marginal. Check that the router you choose has sockets for one.

Which network? The UK has four physical mobile networks: EE, Vodafone, Three and O2. Vodafone and Three have merged, and the combined company trades as VodafoneThree ³. Many cheaper brands are "virtual" operators that rent capacity on one of those networks. On current listings, SMARTY and iD Mobile use Three's network; giffgaff and Tesco Mobile use O2; Lebara, Asda Mobile and Talkmobile use Vodafone; Lycamobile and spusu use EE ². A virtual operator will not give you coverage its host network lacks.

A useful rule: put the backup on a different network from your everyday phone. If the backup's network has a local problem, your phone's hotspot is then a second fallback. If you use a provider add-on, it will use that provider's own mobile network: EE's uses EE 4G ¹⁷ and Vodafone's uses Vodafone 4G ¹⁶, so check that network's signal at your address before you sign up.

Hardware options compared

Three notes on that table.

The backup mode is what you are paying for. A 4G router on its own simply gives you mobile broadband. For failover, it must be able to treat your fixed line as the main connection and the SIM as the standby. TP-Link's 4G and 5G routers do this in what the company calls Wireless Router Mode, where the mobile network is used "as a backup solution" when the main service fails ¹⁴. The DrayTek 2927 "L" models have a built-in 4G modem with two SIM slots and automatic failover ¹⁸. Check the manual of any model before you buy; not every router with a SIM slot can do it.

Reviews and forums are worth reading. The Archer MR600 has been reviewed as an affordable way to add 4G failover to an existing connection ²⁰, but TP-Link's own community pages document cases where the switch to mobile, or the switch back, did not happen as expected ¹⁵. That is an argument for testing your setup properly, which the step-by-step setup guide covers.

Provider add-ons are compared separately. They suit some households well and are covered in ISP backup vs DIY vs satellite.

SIMs and data plans

The right plan depends on how often you expect to be on the backup and how much you would use it.

Read the small print for these points before you order:

• Is router use allowed? Some phone plans restrict tethering or use in a router. Data-only SIMs avoid the question.
• Is "unlimited" unlimited? Some plans carry a fair-use ceiling; Lycamobile's unlimited plan is listed with a 450 GB limit, for example ².
• Is the speed capped? Some unlimited tariffs are sold with a maximum speed, such as EE plans listed at 10 Mbps and 100 Mbps ². Ten is still enough for calls.
• What happens each April? Many contracts rise by a fixed amount every year. One Three 5G broadband deal at £16 a month was due to rise to £19.50 and then £23 over two Aprils ¹⁹.
• Does PAYG data expire if unused? Check the expiry date and any inactivity rule so the SIM is alive on the day you need it.

A standalone 5G home broadband hub does not fail over by itself. To make it automatic you add a dual-WAN router that manages both connections; the setup guide shows how.

How much data a backup really needs

Zoom publishes the bandwidth its calls need ⁷. Converting those rates into data per hour is simple: multiply megabits per second by 450 to get megabytes per hour in one direction, then double it because you send as well as receive.

These are calculations from published bandwidth figures, not measurements, and other platforms will differ. They are a fair planning basis.

On that basis, a working day with three hours of HD video calls uses roughly 3.3 GB for the calls. Email, documents and web browsing add comparatively little. One person working through a five-day outage might therefore use in the region of 20 GB. A 24 GB pay-as-you-go pack covers that once, with little to spare.

Two things break the estimate. One is other people: a household that carries on streaming video in the evening will use far more than a single home worker. The other is devices doing things you did not ask for, such as cloud photo backups and operating-system updates. For context, Vodafone's provider backup comes with 100 GB a month ¹⁶ and EE's backup device contains an unlimited-data SIM ¹⁷. If you choose a capped plan, the setup guide explains how to stop devices wasting it.

The limits: shared addresses, congestion and power

You usually cannot accept inbound connections. Mobile networks do not normally give each customer a public IP address of their own. They place many customers behind one shared address, an arrangement called carrier-grade NAT (CGNAT). Anything that starts from your side works as usual: browsing, calls, streaming, most VPNs. Anything that tries to reach in from outside does not: remote access to a home server, port forwarding for cameras, some older VPN and phone-system setups. EE's community support states that its mobile network does not provide a public address outside CGNAT ⁸, and Three customers have reported being moved behind CGNAT on 5G broadband ⁹. Cameras and smart-home kit that connect outwards to a cloud service are unaffected. If you need inbound access during an outage, see the options in the business guide.

Speeds depend on who else is using the mast. A mobile cell is shared by everyone nearby. When a local broadband fault pushes many households on to mobile at once, the backup slows for all of them. Vodafone says of its own backup that speed and consistency vary with location, coverage and demand ¹⁶.

Masts need electricity too. The amount of battery backup at mobile sites varies by operator, both in how many sites have it and for how long ¹². Ofcom's resilience guidance, revised on 16 June 2026, sets out expectations for operators but does not specify a number of hours ¹⁰¹¹. A mobile backup with a battery at your end will ride out a power cut on your street. In a wide-area cut, it may not.

Provider add-ons may be for emergencies only. Vodafone's terms describe its dongle as intended for a total loss of fixed-line service, and say it is not a direct replacement for the line ¹⁶.

None of this argues against mobile backup. It argues for knowing what it will and will not do before the day you need it.

Two-year cost: three worked examples

These examples use the November 2026 prices cited above. They exclude a battery, which you need only if power cuts are part of your risk.

A. The occasional-use kit. A 4G router at £89 to £99 ¹³ plus a 24 GB, 24-month pay-as-you-go data pack, which retailers list at roughly £35 to £45. Total over two years: about £125 to £144, or roughly £5 to £6 a month. Automatic, but you must watch the data.

B. The always-ready kit. The same router plus a rolling unlimited SIM at £16 a month ². Total: £89 to £99, plus £384 for 24 months, so about £473 to £483, or roughly £20 a month. No data anxiety, and you can cancel the SIM.

C. The second line. Three's 5G Home Broadband at £13 a month for 24 months is £312 before annual price rises ³¹⁹, router included. Add a wired dual-WAN router such as the TP-Link ER605, listed at about £49 ²¹, if you want automatic failover. This gives you two usable connections, not one and a spare.

For comparison, EE's Connectivity Backup add-on at £10 a month comes to £240 over two years ²², with no hardware to buy and nothing to configure, but it is only available to EE broadband customers. The full comparison is in ISP backup vs DIY vs satellite.

FAQ

Sources

Checked 13 November 2026.

1. Ofcom, "Connected Nations update: Spring 2026" (data as of January 2026), 13 May 2026: ofcom.org.uk
2. Ken's Tech Tips, "Unlimited data SIM plans" (listings and host networks, viewed November 2026): kenstechtips.com
3. ISPreview, "Three UK cuts unlimited 5G Home Broadband plan price to just £13pm", 6 November 2026: ispreview.co.uk
4. Broadband.co.uk, "5G home broadband deals" (advertised average speeds): broadband.co.uk
5. TechRadar, report on Vodafone's monthly 5G broadband launch, 2026: techradar.com
6. Three, "Contract summary: Pay As You Go Mobile Broadband SIMs": three.co.uk
7. Zoom, system and bandwidth requirements: developers.zoom.us (bandwidth table as reproduced at colum.teamdynamix.com)
8. EE Community, thread on public IP addresses and CGNAT on EE mobile broadband: community.ee.co.uk
9. Three Community, "5G suddenly switched to CGNAT??": community.three.co.uk
10. Ofcom, "Statement: Network and Service Resilience Guidance" (last updated 16 June 2026): ofcom.org.uk
11. Osborne Clarke, "Telecoms: UK Regulatory Outlook July 2026", 29 July 2026: osborneclarke.com
12. Ofcom, "Resilience guidance consultation and Call for Input on mobile RAN power back up", December 2023: ofcom.org.uk
13. PriceSpy UK, TP-Link 4G/5G router listings (viewed November 2026): pricespy.co.uk
14. TP-Link, "How to set up 3G/4G/5G Backup on TP-Link LTE router under wireless router mode": omadanetworks.com
15. TP-Link Community, "3G/4G Backup failover issue for LTE Gateway/Deco 4G/5G products": community.tp-link.com
16. Vodafone, "Pro Broadband" (4G Broadband Back-up terms): vodafone.co.uk
17. EE, "Connectivity Backup" terms and conditions, December 2025: ee.co.uk
18. ProVu, "DrayTek Vigor 2927 Router Series" (specifications and recommended retail prices): provu.co.uk
19. ISPreview, "Three UK Mobile Launch Summer 5G Home Broadband Deals from £18pm", 2 June 2026: ispreview.co.uk
20. Expert Reviews, "TP-Link Archer MR600 V2 review": expertreviews.co.uk
21. Mighty Gadget, "Best dual WAN routers" (TP-Link ER605 listing): mightygadget.co.uk
22. EE, "EE Home Price Guide" (add-on prices, April 2026): ee.co.uk
23. Vodafone, "5G Broadband" (plan prices, checked 13 November 2026): vodafone.co.uk

General information for UK households and small businesses, not legal, financial or technical advice. Facts checked on 13 November 2026; prices, coverage and rules change, so confirm the details with a provider before you buy.

Next guideBusiness Broadband Backup: Failover, Dual-WAN and SLAs for Small Firms